1. Field of the Invention
This invention relates to organopolysiloxane compositions and more particularly, to curable organopolysiloxane compositions whose curing speed is high and which are capable of yielding a cured silicone release composition having good adhesion to a variety of substrates. The invention also relates to a cured product of the composition.
2. Description of the Prior Art
For the purpose of preventing adhesion or cohesion between substrates such as paper sheets or plastic films and self-adhesive sheets, usual practice is to impart release properties to the surface of the substrate by formation of the film of a silicone composition on the substrate surface.
Several procedures of forming the silicone film on the substrate surface are known including:
(1) a method wherein a release film is formed by addition reaction of organopolysiloxanes having an aliphatic unsaturated bond or bonds and organohydrogenpolysiloxanes in the presence of platinum compounds; and
(2) a method wherein a release film is formed by condensation reaction of organopolysiloxanes by use of organic metal salt catalysts such as organic tin compounds.
The silicone compositions used in these procedures can yield films by application of heat and are thus of a thermally curable type. Depending on the nature of the composition, these compositions can be classified into a solvent type where the ingredients are dissolved in organic solvents such as toluene, an emulsion type where the ingredients are emulsified, and a solvent-free type which makes use of silicones alone.
From the standpoint of industrial production, the first method wherein the curing speed is significantly higher than the second method has been widely employed. As an organohydrogenpolysiloxane serving as a crosslinking agent in the addition-reactive siloxane composition used in the first method, methylhydrogenpolysiloxane of the following formula (1) wherein m and n are, respectively, a positive value has been widely used ##STR1##
In order to enhance the curability, there has been proposed, for example, in Japanese Laid-open Patent Application No. 61-235461 an organohydrogenpolysiloxane of the formula, (R.sup.1 SiO.sub.1.5).sub.m (R.sup.2.sub.2 HSiO.sub.0.5).sub.n, wherein each R.sup.1 and each R.sup.2 may be the same or different and represent an unsubstituted or substituted monovalent hydrocarbon group except for aliphatic unsaturated hydrocarbon groups and m and n satisfy the relation of 0.1&lt;n/m&lt;3. As will be apparent from the above, the above organohydrogenpolysiloxane is of the type which consists of the trifunctional siloxane units and the monofunctional siloxane units.
Although the curability is enhanced, adhesion to substrates is lowered. This makes it difficult to use the organohydrogenpolysiloxane singly, thus leading to the drawback that this siloxane has to be used in combination with the siloxane of the above-indicated formula.